The invention relates to a blade bit to be attached to a chuck in an envelope surface of a crusher rotor, the blade bit having four corners and arranged for being attached to the chuck such that an angular-shaped tip of the blade bit pointing outwardly from the envelope surface, substantially in the radial direction of the rotor, whereby the rear surface of the blade bit, which acts as its attachment surface to the chuck, comprises a support surface, that prevents the blade bit from rotating and that also enables sliding of the blade bit towards the envelope surface, when the blade bit is being attached, until the blade bit is supported to the envelope surface.
The crushers typically employ dynamic and static blades. All blades may also be dynamic.
The blades may be made of various materials, such as steels. Blade properties may be improved in various ways, such as thermal treatments and coatings. The thermal treatment allows sufficient endurance and functionality to be achieved against wear and impacts. The blades must also stay sharp in operations where cutting is required.
The blades may also be coated by using various methods that include, for instance, detonation, PTA (Plasma Transferred Arc) spraying, HVOF (High Velocity Oxygen Fuel Thermal Spray Process), laser hybrid welding/melting processes, when coatings used are typically powders, in which carbides and metal powders are combined. For welding it is also possible to use MIG, MAG and TIG welding, metal arc welding and various soldering methods.
The blades may be attached to chuck structures of a crusher rotor with bolted joints or other attachment arrangements.
When crushing materials that are elastic or soft, it is common to use blade technology that is based on cutting the material. For a successful operation it is essential that cutting allowance is as small as possible. In practice, this requirement also necessitates allowance adjustment so as to compensate for wearing.
It is known technology to use as cutting blades replaceable blade bits having the basic shape of a square and the front surface that is either flat or concave. They are attached to chucks on the envelope surface of the crusher rotor by using a screw passing through the chuck such that it utilizes the blade bit as a nut. A corner of the blade bit square points thus outwardly from the envelope surface in the radial direction of the rotor. Lateral positioning is typically provided by means of a V-groove on the rotor surface and a large hole in the chuck.
As the tip of the blade bit and the cutting edges downwardly therefrom wear (become dull), the cutting capacity degrades and a need for force increases. In that case the blade bit is rotated 90 degrees or 180 degrees and consequently sharp edges and a tip will be in use.
After rotation, the blade surfaces used for support are typically worn and consequently the guiding effect in the V-groove of the envelope surface of the crusher rotor is not necessarily appropriate. The blade may also assume a slightly slanted position, if one blade bit side is more worn than the other. This, in turn, has a consequence that blade allowance adjustment, which often takes place by adjusting blocks consisting of several blade bits, cannot achieve the desired allowance. The slanted blade bit defines the allowance of the whole adjustment block, and typically, the allowance is clearly larger than desired.